Question

As a pendulum swings, the amounts of potential and kinetic energy change. Does the amount of mechanical energy change?

Answer 1

No, the mechanical energy does not change if it is ideal.

We define mechanical energy as the sum of kinetic energy and potential energy

ME = PE + KE

When the pendulum swings, potential energy is converted to kinetic energy and vise versa. But the sum of both remains constant, which is the mechanical energy.